Re: [PATCH 1/2] mm/large system hash: use vmalloc for size > MAX_ORDER when !hashdist

[Andrew Morton <akpm@linux-foundation.org>]

On Thu,  6 Jun 2019 00:48:13 +1000 Nicholas Piggin <npiggin@gmail.com> wrote:

> The kernel currently clamps large system hashes to MAX_ORDER when
> hashdist is not set, which is rather arbitrary.
> 
> vmalloc space is limited on 32-bit machines, but this shouldn't
> result in much more used because of small physical memory limiting
> system hash sizes.
> 
> Include "vmalloc" or "linear" in the kernel log message.
> 
> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> ---
> 
> This is a better solution than the previous one for the case of !NUMA
> systems running on CONFIG_NUMA kernels, we can clear the default
> hashdist early and have everything allocated out of the linear map.
> 
> The hugepage vmap series I will post later, but it's quite
> independent from this improvement.
> 
> ...
>
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -7966,6 +7966,7 @@ void *__init alloc_large_system_hash(const char *tablename,
>  	unsigned long log2qty, size;
>  	void *table = NULL;
>  	gfp_t gfp_flags;
> +	bool virt;
>  
>  	/* allow the kernel cmdline to have a say */
>  	if (!numentries) {
> @@ -8022,6 +8023,7 @@ void *__init alloc_large_system_hash(const char *tablename,
>  
>  	gfp_flags = (flags & HASH_ZERO) ? GFP_ATOMIC | __GFP_ZERO : GFP_ATOMIC;
>  	do {
> +		virt = false;
>  		size = bucketsize << log2qty;
>  		if (flags & HASH_EARLY) {
>  			if (flags & HASH_ZERO)
> @@ -8029,26 +8031,26 @@ void *__init alloc_large_system_hash(const char *tablename,
>  			else
>  				table = memblock_alloc_raw(size,
>  							   SMP_CACHE_BYTES);
> -		} else if (hashdist) {
> +		} else if (get_order(size) >= MAX_ORDER || hashdist) {
>  			table = __vmalloc(size, gfp_flags, PAGE_KERNEL);
> +			virt = true;
>  		} else {
>  			/*
>  			 * If bucketsize is not a power-of-two, we may free
>  			 * some pages at the end of hash table which
>  			 * alloc_pages_exact() automatically does
>  			 */
> -			if (get_order(size) < MAX_ORDER) {
> -				table = alloc_pages_exact(size, gfp_flags);
> -				kmemleak_alloc(table, size, 1, gfp_flags);
> -			}
> +			table = alloc_pages_exact(size, gfp_flags);
> +			kmemleak_alloc(table, size, 1, gfp_flags);
>  		}
>  	} while (!table && size > PAGE_SIZE && --log2qty);
>  
>  	if (!table)
>  		panic("Failed to allocate %s hash table\n", tablename);
>  
> -	pr_info("%s hash table entries: %ld (order: %d, %lu bytes)\n",
> -		tablename, 1UL << log2qty, ilog2(size) - PAGE_SHIFT, size);
> +	pr_info("%s hash table entries: %ld (order: %d, %lu bytes, %s)\n",
> +		tablename, 1UL << log2qty, ilog2(size) - PAGE_SHIFT, size,
> +		virt ? "vmalloc" : "linear");

Could remove `bool virt' and use is_vmalloc_addr() in the printk?